1. Field of the Invention
The present invention relates to a broadband wireless communication system. More particularly, the present invention relates to an apparatus and a method for relocating a persistently allocated resource in the broadband wireless communication system.
2. Description of the Related Art
A 4th Generation (4G) communication system, which is a future-generation communication system, aims to provide users with services of various Quality of Service (QoS) levels at a transfer rate of about 100 Mbps. Its representative examples include an Institute of Electrical and Electronics Engineers (IEEE) 802.16 communication system. The IEEE 802.16 communication system adopts an Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) scheme to support a broadband transmission network in physical channels.
In the broadband wireless communication system such as the IEEE 802.16 system, a base station allocates resources to terminals to transmit and receive packets. The base station transmits a MAP message indicative of the resource allocation result such as location, size, modulation scheme, and coding rate of the allocated resource, to the terminal over a downlink channel. A message indicative of the resource allocation information for uplink communication and a message indicative of the resource allocation result for downlink communication are separately constituted. The unit of the information required for one resource information is referred to as a MAP Information Element (IE).
The resource allocation targets the resources in a certain region. Since general data packets are allocated at regular intervals, the related MAP IE is transmitted at the regular intervals. In the case of Voice over Internet Protocol (VoIP) service or synchronous Hybrid Automatic Repeat reQuest (HARQ) with periodic packet transmission, the transmission of the MAP IE in every packet delivery causes an unnecessary waste of resources. Accordingly, the packet of the periodic transmission period, such as VoIP packet or synchronous HARQ packet, can adopt a fixed allocation scheme which reduces the waste of the resources in the MAP IE by persistently allocating the resources. According to the fixed allocation, in the downlink communication, the MAP IE and the packet are transferred only at the initial resource allocation and then the packet is transmitted without the MAP IE. Hence, the terminal using the persistently allocated resource continues to use the persistently allocated resource without the MAP IE until allocation release information or allocation change information is received.
If the transmission periods of the synchronous HARQ packet and the VoIP packet are different from each other, the persistently allocated resources may collide with each other. For example, given the VoIP packet in a two-frame period and the synchronous HARQ packet in a one-frame period, the packets collide with each other as illustrated in FIG. 1. FIG. 1 illustrates a collision between persistently allocated resources in a broadband wireless communication system according to the conventional art. In FIG. 1, the first VoIP packet 111 is transmitted in a frame #1. After the period of the VoIP packet passes by, a second VoIP packet 113 is transmitted in a frame #3. Next, in a frame #4, a HARQ initial transmit packet 121 is transmitted using the resource at the same location as the resource used for the first VoIP packet 111 and the second VoIP packet 113. It is assumed that the reception of the HARQ initial transmit packet 121 fails. Hence, in a frame #5, it is necessary to retransmit a packet for the HARQ initial transmit packet 121. Simultaneously, a third VoIP packet needs to transmit as well in the frame #5. That is, the resources for retransmitting the packet and transmitting the third VoIP packet are subject to the collision.
As discussed above, when the fixed allocation of the different periods is applied to the broadband wireless communication system, the collision between the resources can occur. As a result, the terminals cannot successfully receive the packets. Thus, what is needed is a method for preventing the collision between the persistently allocated resources.